1. Field of the Invention
The present invention relates to a shock detection device, a shock detection method, a shock detection program and a disk drive equipped with such a shock detection device, for detecting a shock applied to a magnetic disk drive or the like.
2. Description of the Related Art
Magnetic disk drives available for mobile use are generally provided with a shock detection device for detecting a shock from the outside in consideration of use environments. The magnetic disk drives are constructed in such a manner that they stop writing data upon detection of a shock from the outside.
FIG. 7 is a block diagram that shows one example of the configuration of a known magnetic disk drive. As shown in FIG. 7, the known magnetic disk drive includes an HDC (Hard Disc Controller) 1, a write-protection circuit 2, a shock detection device 3, an off-track error determining part 4, an R/W (Read/Write) circuit 5, a head amplifier circuit 6, an R/W head 7, and a servo circuit 8.
Here, reference will be made to the organization of data on a magnetic disk medium using a data surface servo system. FIG. 8 is a view showing the arrangement of servo areas and data areas on the magnetic disk medium. As shown in FIG. 8, a plurality of tracks exist on the magnetic disk medium in a radial direction thereof, and the servo areas and the data areas are also arranged on the medium alternately in a rotational direction thereof.
The information of radial locations of the disk medium is successively written beforehand in the servo areas in a radial direction of the disk medium. If the servo areas are decoded in any radial position of the disk medium, a position error signal can be acquired. The position error signal represents a relative position in a radial direction of the disk medium from the center of a target track. Each time a servo area in the rotational direction of the disk medium is detected, the decoding of that servo area is executed. The interval of decoding the successive servo areas is a servo sampling interval.
Next, reference will be made to the operation of the known magnetic disk drive. When the HDC 1 receives a read/write instruction for reading or writing data from an I/F (Interface) host, it outputs a control signal for controlling the R/W circuit 5 and data from the I/F host to the R/W circuit 5 in the case of writing, whereas it outputs a control signal for controlling the R/W circuit 5 to the R/W circuit 5, and data from the R/W circuit 5 to the I/F host in the case of reading.
In addition, the HDC 1 outputs a servo gate signal representative of the timing of driving the servo circuit 8 to the R/W circuit 5. Also, upon writing data, the HDC 1 outputs a write gate signal representative of the timing at which data is written into the magnetic disk medium to the write-protection circuit 2.
Upon detecting a shock from the outside, the shock detection device 3 outputs a shock detection signal to the write-protection circuit 2.
When there takes place an off-track error, the off-track error determining part 4 outputs an off-track error determining signal to the write-protection circuit 2. An off-track error means that the R/W head 7 comes off from a target track to another track, and when a position error signal exceeds an off-track error slice value, it is determined that an off-track error has occurred.
The write-protection circuit 2 determines, based on the shock detection signal and the off-track error determining signal, whether a write gate signal is output from the HDC 1 to the R/W circuit 5. Upon receiving the write-protection signal from the off-track error determining part 4 or the shock detection signal from the shock detection device 3, the write-protection circuit 2 determines that the disk drive is in a condition unsuitable for writing, and stops outputting the write gate signal to the R/W circuit 5, whereas the write-protection circuit 2 outputs the write gate signal from the HDC 1 to the R/W circuit 5 at other times.
The R/W circuit 5 drives the servo circuit 8 in accordance with the timing of the servo gate signal and the control signal from the HDC 1. The servo circuit 8 performs the positioning of the R/W head 7, etc.
Thereafter, the R/W circuit 5 performs the reading or writing of data by means of the head amplifier circuit 6 and the R/W head 7 in accordance with the timing of the write gate signal and the control signal. Additionally, the R/W circuit 5 outputs the position error signal reproduced from the R/W head 7 to the off-track error determining part 4.
Now, reference will be made to the configuration of the known shock detection device. FIG. 9 is a block diagram showing one example of the configuration of the known shock detection device. As shown in FIG. 9, the known shock detection device 3 includes a shock sensor 31, an amplifier circuit 32, a shock detection slice value setting part 33, and a comparator 34.
Next, reference will be made to the operation of the known shock detection device. The shock sensor 31 is comprised of a piezoelectric element that serves to convert an acceleration into a corresponding voltage for instance, and it detects a shock applied thereto from the outside and outputs a corresponding voltage to the amplifier circuit 32.
The amplifier circuit 32 amplifies the output of the shock sensor 31 by a prescribed value, and outputs it to the comparator 34 as a shock sensor signal.
The shock detection slice value setting part 33 is comprised of an MPU (Micro Processing Unit) for instance, and it sets a shock detection slice value, which is a threshold for the shock sensor signal 31, and outputs it to the comparator 34.
The comparator 34 makes a comparison between the shock sensor signal and the shock detection slice value, and outputs a shock detection signal to the write-protection circuit 2 when the shock sensor signal exceeds the shock detection slice value. In the above manner, the known shock detection device 3 detects a shock from the outside.
Moreover, there has also been known another disk drive equipped with a shock sensor in which the frequency dependence of a shock sensor output can be reduced, thereby decreasing errors in the operation of stopping writing and providing shock protection of data in an accurate manner (for example, see a first patent document: Japanese patent application laid-open No. H06-333325 (pages 3 and 4, and FIG. 1)).
In the above-mentioned known shock detection device as shown in FIG. 9, however, there arises a problem that if the shock detection slice value is set to be low so as to detect a slight or weak shock, mis-detection of a shock might be caused due to noise in the shock sensor signal, resulting in reduced writing performance.
Therefore, in the known shock detection device, the shock detection slice value is generally set to be high. In this case, however, there arises another problem that if a position error signal generated upon application of a slight shock to the disk drive fails to be detected between servo samplings, writing might be carried out off-track or out of a target track, thus resulting in the deletion of data on an adjacent track.